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Photocatalytic decolorization of three commercial dyes using a new heteropolyoxotantalate catalyst.

ABSTRACT: The decolorization of commercial dyes is still a pertinent issue since these azo dyes are relatively resistant to conventional biological treatment methods. It is well known that polyoxometalates can absorb light in UV-Vis range that delivers electrons to the reducible species resulting in the decomposition of organic compounds. In this paper, we present the third heteropolyoxotantalate under conventional synthetic conditions in the presence of hydrogen peroxide. The compound has been thoroughly characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy, thermogravimetric analysis and powder X-ray diffraction. The polyanion incorporates two 3-peroxotantalo-2-phosphate clusters that are linked together by four oxygen bridges. In addition, the photocatalytic activities of the title compound 1a were investigated. After 270 min irradiation, about 90% of Rhodamine B (RhB) was removed in the presence of 1a while the degradation of RhB could be negligible in the absence of 1a, indicating it can be a promising catalyst candidate for decolorization of organic dyes. Also, photocatalytic experiment for hydrogen generation was studied, and the results show that the H2 evolution rate is 3383 µmol h-1 g-1 for compound 1a (100 mg) over 6 h with the corresponding turnover number of 432.

SUBMITTER: Wang Y

PROVIDER: S-EPMC6731712 | biostudies-literature | 2019 Aug

REPOSITORIES: biostudies-literature

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Photocatalytic decolorization of three commercial dyes using a new heteropolyoxotantalate catalyst.

Wang Yansong Y Zhou Zhimin Z

Royal Society open science 20190828 8

The decolorization of commercial dyes is still a pertinent issue since these azo dyes are relatively resistant to conventional biological treatment methods. It is well known that polyoxometalates can absorb light in UV-Vis range that delivers electrons to the reducible species resulting in the decomposition of organic compounds. In this paper, we present the third heteropolyoxotantalate under conventional synthetic conditions in the presence of hydrogen peroxide. The compound has been thoroughly ...[more]

PMID: 31598227

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Project description:Titania nanotube (TNT) powder was prepared by rapid breakdown anodization (RBA) in a perchloric acid electrolyte. The photocatalytic efficiency of the as-prepared and powders annealed at temperatures between 250 and 550 °C was tested under UV and natural sunlight irradiation by decolorization of both anionic and cationic organic dyes, i.e., methyl orange (MO) and rhodamine B (RhB), as model pollutants. The tubular structure of the nanotubes was retained up to 250 °C, while at 350 °C and above, the nanotubes transformed into nanorods and nanoparticles. Depending on the annealing temperature, the TNTs consist of anatase, mixed anatase/brookite, or anatase/rutile phases. The bandgap of the as-prepared nanotubes is 3.04 eV, and it shifts towards the visible light region upon annealing. The X-ray photoelectron spectroscopy (XPS) results show the presence of titania and impurities including chlorine on the surface of the TNTs. The atomic ratio of Ti/O remains unchanged for the annealed TNTs, but the concentration of chlorine decreases with temperature. The photoluminescence (PL) indicate high electron-hole recombination for the as-prepared TNTs, probably due to the residual impurities, low crystallinity, and vacancies in the structure, while the highest photocurrent was observed for the TNT sample annealed at 450 °C. The TNTs induce a small degradation of the dyes under UV light; however, contrary to previous reports, complete decolorization of dyes is observed under sunlight. All TNT samples showed higher decolorization rates under sunlight irradiation than under UV light. The highest reaction rate for the TNT samples was obtained for the as-prepared TNT powder sample under sunlight using RhB (?1 = 1.29 h-1). This is attributed to the bandgap, specific surface area and the crystal structure of the nanotubes. The as-prepared TNTs performed most efficiently for decolorization of RhB and outperformed the reference anatase powder under sunlight irradiation. This could be attributed to the abundance of reactive sites, higher specific surface area, and degradation mechanism of RhB. These RBA TNT photocatalyst powders demonstrate a more efficient use of the sunlight spectrum, making them viable for environmental remediation.

Project description:In this study, the Fe-containing tailings (Fe-TO) ore was reutilized and enriched with FeCl3 as a heterogeneous catalyst for the Fenton process to degrade the organic dyes from aqueous solution. The determinants of the heterogeneous catalytic Fenton system which included iron modification ratio, solution pH, catalyst dosage, H2O2 dosage and initial concentration of organic dyes were systematically investigated. The modification ratio of 15% (w/w of iron), pH of 3, MFe-TO15 dosage of 0.5 g L-1 and H2O2 dosage of 840 mg L-1 were chosen as the best operational conditions for Fenton oxidation of organic dyes. The decolorization efficiency of both MB and RhB by MFe-TO15/H2O2 was higher than that of Fe-TO/H2O2 by about two times. The kinetic study showed the degradation of organic dyes well fitted the pseudo-first-order kinetic model with apparent constant rate values (K d) following the same sequence as the degradation efficiency of organic dyes. The degradation mechanism of dyes could be attributed to adsorption due to the good-development in textural properties of the iron modified catalyst (MFe-TO) with an increase in BET surface area, pore volume and pore diameter of, respectively, 2, 5 and 5 times and leaching iron through homogeneous Fenton reaction. However, the oxidation process occurring on the MFe-TO15's surface by heterogeneous Fenton reaction which enhanced decomposition of H2O2 for continuous generation of hydroxyl radicals was the main mechanism. The key role of *OH radical in oxidation of organic dyes was further ascertained by the remarkable drop in the decolorization of both organic dyes when the various radical-scavengers, including tert-butanol and chloride were supplemented into Fenton systems. A good stability of the catalyst was obtained through leaching test with low leaching iron ratio. The applied modified catalyst remained stable through three consecutive runs. From these findings, it can be concluded that the modified material can be applied as a feasible, inexpensive and highly effective catalyst for removal of persistent organic compounds from wastewater.

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Photocatalytic decolorization of three commercial dyes using a new heteropolyoxotantalate catalyst.

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Photocatalytic decolorization of three commercial dyes using a new heteropolyoxotantalate catalyst.

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